Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into a plurality of individual device chips along a plurality of division lines, the division lines being formed on the front side of the wafer to thereby define a plurality of separate regions where a plurality of devices corresponding to the device chips are formed.
Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of devices such as ICs and LSIs are formed. These regions are divided from each other by cutting the semiconductor wafer along the division lines, thereby producing a plurality of individual device chips corresponding to the devices.
As a method of dividing the wafer along the division lines, a laser processing method has been tried. The laser processing method uses a pulsed laser beam having a transmission wavelength to the wafer, wherein the pulsed laser beam is applied to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer in a subject area to be divided. That is, the wafer dividing method using this laser processing method includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side of the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each division line, and next applying an external force to the wafer along each division line where the modified layer is formed to be reduced in strength, thereby breaking the wafer along each division line (see Japanese Patent No. 3408805, for example).
As another method of dividing the wafer along the division lines, there has been put into practical use a technique including the steps of applying a pulsed laser beam having an absorption wavelength to the wafer along each division line, thereby forming a laser processed groove along each division line by ablation, and next applying an external force to the wafer along each division line where the laser processed groove is formed as a break start point, thereby breaking the wafer along each division line (see Japanese Patent Laid-Open No. 1998-305420, for example).